In known concertina type doors, the door comprises a horizontally stiff vertically flexible curtain constituted by a series of hinged horizontal panels, or else by a flexible sheet which is stiffened at regular intervals by horizontal stiffener rods. Door-lifting belts each have one end fixed to the bottom of the curtain and the other end fixed to a belt-winding shaft which is rotated under motor control. Preferably, the door-lifting belts pass through guides disposed at intervals up the curtain, e.g. on at least some of the stiffener bars or on at least some of the hinges interconnecting consecutive panels. Each end of the bottom panel (if the door is made of panels), or each end of the bottom stiffener bar and of some of the other stiffener bars (if the door is made of a curtain with stiffener bars), is fitted with a wheel for running along a guide running up the side of the door in the corresponding door riser.
In a conventional embodiment of the belt-winding shaft, the shaft is disposed above the door and rotates in bearings which are fixed to the inside of a metal channel-section bar with the web of the channel section being horizontal and on top, said bar constituting a door lintel. The motor for driving the shaft is fixed along one of the door risers near to the top of the door. The motor shaft is perpendicular to the belt-winding shaft and these two shafts are coupled together by an angle transmission which may also include gear ratio step-down means.
This conventional embodiment suffers from several drawbacks. Firstly, the disposition of the channel-section beam is not entirely satisfactory from the safety point of view, by virtue of its web being on top. It frequently happens in industrial installations that a door of this type is opened and closed several hundred times a day, thereby eventually wearing out and maybe even breaking some of the parts housed in the beam. It can then happen that broken parts, and/or loose nuts or screws, fall out from the beam and that such falling debris can lead to accidents.
Secondly, placing the motor along a door riser makes maintenance, and where necessary repair, difficult. It is often necessary to lower the motor to ground level in order to perform maintenance or repair work thereon.
Finally, if the door is to be used under harsh climatic conditions, it should be observed that nothing is provided to protect the drive means against the effects of condensation and of frost. Freezing condensation may jam some types of mechanical transmission, thereby making the door unusable.
Preferred embodiments of the present invention solve the above-mentioed drawbacks by providing a fixing and protective housing for the drive means of such concerntina type doors.